(1) Field of the Invention
The present invention relates to a method for polarization treatment of a piezoelectric/electrostrictive film type chip which is integrated piezoelectric/electrostrictive film type elements.
(2) Description of Prior Art
In recent years, there has been known, as a mechanism for increasing the pressure inside a pressure room formed in a material, a piezoelectric/electrostrictive film type element which is fixed on the wall of the pressure room and which can change the volume of the pressure room owing to the displacement of the piezoelectric/electrostrictive section. Such a piezoelectric/electrostrictive film type element is being used, for example, as the ink pump of a print head used in an ink jet printer.
The print head is formed by integrating a plurality of piezoelectric/electrostrictive film type elements to produce an piezoelectric/electrostrictive film type chip and joining the chip with an ink nozzle member. Prior to the joining, the piezoelectric/electrostrictive film type chip is generally subjected to a polarization treatment to polarize it to a given direction.
FIG. 2 is a sectional view showing part of a piezoelectric/electrostrictive film type element. On a diaphragm 10 are laminated a lower electrode 11, a piezoelectric/electrostrictive layer 12 and an upper electrode 13 in this order, whereby a piezoelectric/electrostrictive film type element 15 is constituted. Such a piezoelectric/electrostrictive film type element 15 is integrated by, for example, 66 elements, whereby a piezoelectric/electrostrictive film type chip 20 as shown in FIG. 3 is formed. In the piezoelectric/electrostrictive film type chip 20, the piezoelectric/electrostrictive layers 12 of the piezoelectric/electrostrictive film type elements 15 are formed each independently, but the upper electrodes 13 and the lower electrodes 11 are respectively connected between the piezoelectric/electrostrictive film type elements 15.
The polarization treatment to such a piezoelectric/electrostrictive film type chip 20 has been conducted by, as shown in FIG. 3, forming a circuit 22 for polarization treatment between the upper electrodes 13 and the lower electrodes 11 of the piezoelectric/electrostrictive film type elements 15 and applying a given voltage to the circuit. In FIG. 3, R is a load resistance used in the circuit 22 for polarization treatment, and 23 is an electric source.
When the piezoelectric/electrostrictive film type chip 20 is subjected to a polarization treatment as above, however, dielectric breakdown arises in the chip 20 when the piezoelectric/electrostrictive layer 12 has defects. When the defects are large and the dielectric breakdown is high, those piezoelectric/electrostrictive film type elements having such defects become unusable. A study by the present inventor indicated that when the dielectric breakdown is low, the piezoelectric/electrostrictive film type elements showing such dielectric breakdown are hardly affected in the performance and are sufficiently usable as piezoelectric/electrostrictive film type elements.